This invention relates to protein-rich products of the origin of brewer's spent grain (hereinafter referred to as BSG). The protein-rich products are suited as feed for farm, animals and cultured fish, and are quite useful as food material such as starting materials for proteinaceous nutrients and seasonings.
As a vegetable, protein-rich product, soybean and defatted soybean are most widely used. Especially defatted soybean is the standard of vegetable protein source. However, soybean-producing districts are localized in the world, and a problem of short supply of soybean can arise on account of unseasonable weather. In addition, soybean supply in a number of countries almost completely depends upon import, with the import price varying depending upon various factors. Hence vegetable protein sources alternative to soybean or defatted one, which can be supplied stably at low prices, are needed.
On the other hand, since BSG, which is a by-product of beer production, contains protein in an amount of as low as about 25 % based on dry weight and contains fibrous materials and nitrogen-free solubles in a sum amount of as high as nearly 60 %, its use has been limited at present to ruminants such as cattle and sheep. Accordingly, it has been desired to separate a protein-rich fraction from BSG.
In order to increase a protein content, attempts have been made to mill and sieve dry BSG (U.S. Pat. Nos. 4,377,601 and 4,547,382). In this process, husks become so fine in the grinding step that separation thereof from a protein-containing fraction becomes difficult, and the protein content of the resulting product is still as low as 30 to 40% by weight based on dry weight, and thus the product is still insufficient as a protein source. In addition, the process has another defect in that, since raw BSG contains water, a large amount of heat energy is required for drying it.
Japanese Unexamined Patent Publication No. 51-129,776 discloses a process of extracting BSG using an alkaline aqueous solution of 11-12 in pH at a temperature of 220 F-250 F (104.degree. C.-121.degree. C.), then precipitating a protein-rich product from the thus-obtained extract by isoelectric precipitation. This process, however, involves decomposition of proteins due to the severe, high-temperature extraction condition, resulting in a decreased yield of proteins and deteriorated quality of the product. In addition, this process requires a large amount of heat energy for extraction at an elevated temperature. Further, the protein-rich product obtained by this process does not contain lipid contained in BSG, with the lipid, important as feed for farm animals and fish, being wasted.